AVHRR Level 1B support information for IR BT uncertainty generation within pygac

Data related to the uncertainty calculation which is used in pygac for HRPT data. Consists of the estimated times of potential solar contamination of the 3.7 micron gain (up to two locations per orbit, gain1_time and gain2_time start/end) as well as the time and 3.7 micron gain where the 4 internal calibration PRTs have a minimum variance as a proxy for the 3.7 micron channel gain over a GAC orbit. See associated documentation for full details when available (project uncerainty document and ATBD from ESA Contract No 4000143514/24/I-DT-lr). Currently the information is not used to update the AVHRR calibration itself but just to estimate uncertainties.